CN105008298A - Blank for dental purposes - Google Patents

Abstract

The invention describes a blank for dental purposes having at least two lithium silicate glass layers and lithium silicate glass ceramic layers bonded to each other, wherein the layers differ in color and the layers are monolithic.

Description

blanks for dental purposes

The present invention relates to blanks for dental purposes with which the optical properties of natural tooth materials can be imitated very well and which, due to their properties, are particularly suitable for the easy preparation of highly esthetic dental restorations with very good mechanical properties thing.

The production of blanks which meet the multifaceted requirements for use in the field of dental engineering presents great difficulties. Such a blank must not only be easy to prepare but it must also be easily moldable and still result in a high strength restoration. Finally, the blank itself already has an appearance close to that of natural tooth material, so that an expensive subsequent veneering of the restoration can be dispensed with.

Blanks for use in dentistry are known in the prior art.

DE 19714178 A1 describes multi-coloured moldings made of ceramic or plastic, which dental restorations can be produced by further mechanical processing. In particular, glass ceramics containing leucite are used as ceramic materials. To produce shaped bodies, different colored powders or granular materials of the starting materials are poured into a die and pressed. For strengthening purposes, the shaped body is also sintered and when it is in its strengthened form, the shaped body is further processed by a CAD/CAM process or a profile milling process to form a dental restoration.

It is known from DE 10336913 A1 that monochrome blanks based on lithium metasilicate glass ceramics can be easily machined and converted by heat treatment into high-strength dental restorations based on lithium disilicate glass ceramics due to their relatively low strength.

EP1859757A2 discloses ZrO2 _- based multicolor blanks obtained by pressing several layers of different colors of powder or granular material and pre-sintering. The resulting blank is formed into a dental molding by milling and grinding. The milling process must be carried out in such a way that the dimensions of the dental preform are increased in order to take into account the shrinkage of the former during the subsequent dense sintering.

EP 2 065 012 A1 describes the production of dental restorations with natural-looking color and opacity gradations made of ceramic moldings, wherein the ceramic moldings have regions in their volume of different colors. Under pressure and heat, these shaped bodies are pressed into mold cavities using a specially designed channel system to form dental restorations. This specialized channel system ensures an ideal distribution of the different colored areas in the restoration volume. The machining of the shaped body to form the restoration is not described.

EP 1 900 341 A1 discloses shaped bodies of layers of different colors which have a specific layer sequence so that color transitions between layers are less perceptible. The shaped body is produced by dry pressing, debonding and sintering of glass ceramic powders of different colors applied one above the other. Dental restorations can be produced from these moldings by means of CAD/CAM technology.

However, such known multicolor blanks produced from layers of powder or granular material also require a sintering step after shaping into the dental restoration in order to obtain the required high strength of the dental restoration. However, this sintering is associated with considerable shrinkage, which has to be taken into account by using enlarged preforms which complicate the process. The known blanks also cannot in any case be processed by machining to form the desired dental restoration, or they are too strong for such processing, leading to excessive wear of the grinding and milling tools employed.

According to the present invention, these problems are avoided. In particular, the object of the present invention is to prepare usable blanks with which the optical appearance of natural tooth materials can be very well imitated, which blanks can easily be given the shape of the desired Afterwards, it can be transformed into precise and high-strength dental restorations without extensive shrinkage.

This object is achieved by blanks according to claims 1 to 8 . Another subject of the invention is the method for producing said blank according to claims 9 to 22, the method for producing a dental restoration according to claims 23 to 25, and the use of said blank according to claim 26 .

The blank for dental purposes according to the invention is characterized in that it has at least 2

Lithium silicate glass layer,

Lithium silicate glass layer with nuclei, or

Lithium metasilicate glass-ceramic layer,

Wherein the layers are of different colors and the layers are integral.

Different colors also mean differences in translucency, opalescence or fluorescence. In particular, a color can be characterized by its Lab value or by a conventional color palette in the dental industry.

Preferably, the layer consists of lithium silicate glass, lithium silicate glass with nuclei or lithium metasilicate glass-ceramic.

The term "integral" refers to a continuous layer, as opposed to a discontinuous layer such as a layer of particles, for example a layer of powder or granular material. The integral layers used according to the invention may also be referred to as solid layers or bulk layers of glass and glass ceramics.

The presence of the integral layer in the blank according to the invention is also responsible for the fact that it can be converted by heat treatment into the desired high-strength dental restoration without substantial shrinkage. In contrast, the discrete layers present in conventional blanks, such as compacted layers of powder or granular material, must still be densely sintered to produce the final dental restoration. However, this dense sintering leads to considerable shrinkage. Therefore, in order to manufacture a precisely fitting dental restoration, it is first necessary to manufacture an enlarged preform of the restoration and then to densely sinter the enlarged preform. However, such programs are complex and error-prone. First of all, the enlargement factor to be selected also needs to be precisely determined in each case, which depends inter alia on the exact sintering conditions used and the type of blank.

The blank according to the invention has at least two integral layers of different colours. In a preferred embodiment, the blank comprises 2 to 10, in particular 2 to 8, such layers. The use of these different layers can easily mimic the visual properties of different regions of the natural tooth material to be replaced. The blanks according to the invention thus successfully meet the increasing demand for starting materials for dental prostheses which meet very high optical requirements.

Preferably, the layer has a thickness of 0.5 to 10.0 mm, and especially 1.0 to 8.0 mm.

The blank has an integral layer of lithium silicate glass, an integral layer of lithium silicate glass with nuclei, or an integral layer of lithium metasilicate glass ceramic.

Lithium silicate glasses are generally produced by melting suitable starting materials. This glass can be transformed into lithium silicate glass with crystal nucleus by heat treatment. The crystal nuclei are those for the crystallization of lithium metasilicate and/or lithium disilicate. Lithium silicate glass with crystal nuclei can be transformed into lithium metasilicate glass ceramics by heat treatment.

Finally, the lithium metasilicate glass-ceramics can be transformed into high-strength lithium disilicate glass-ceramics by further heat treatment. Therefore, lithium silicate glass, lithium silicate glass with crystal nuclei and lithium metasilicate glass ceramics are the precursors of lithium disilicate glass ceramics.

In a preferred embodiment, the blank according to the invention has an integral layer of nucleated lithium silicate glass or an integral layer of lithium metasilicate glass ceramic. Due to their relatively low strength, such blanks can be given the desired shape of the dental restoration particularly easily by machining.

Furthermore, wherein the lithium metasilicate glass-ceramic contains lithium metasilicate as the main crystal phase, and in particular contains more than 5 vol.-%, preferably more than 10 vol.-% and particularly preferably more than 20 vol.-% of lithium metasilicate crystals A blank is preferred. The term "main crystalline phase" means a crystalline phase having the highest proportion by volume compared to other crystalline phases.

It has surprisingly become apparent that the blank according to the invention can not only be easily given the shape of the desired dental restoration by machining, but that it can also be converted into a high-strength dental restoration by heat treatment without substantial shrinkage. This heat treatment forms the crystallization of the high-strength lithium disilicate glass-ceramic in the layer. It was particularly surprising that the crystallization of lithium disilicate occurred not only within the volume of the bulk layer, but also on the boundary surfaces of the layer. This is shown by Figures 2, 4 and 6.

It is also possible firstly to convert the blank according to the invention with a lithium silicate glass layer, a lithium silicate glass layer with crystal nuclei or a lithium metasilicate glass ceramic layer into a corresponding glass ceramic layer with lithium disilicate by heat treatment. of blanks. The blank with the lithium disilicate glass-ceramic layer can then be processed into the desired dental restoration, in particular by machining.

The present invention therefore also relates to a blank for dental purposes, said blank having at least two lithium disilicate glass-ceramic layers bonded to one another,

Wherein the layers are of different colors and the layers are integral.

Preferably, the layer consists of a lithium disilicate glass ceramic.

Wherein the lithium disilicate glass-ceramic comprises lithium disilicate as main crystalline phase, especially the blank that comprises more than 30 vol.-%, preferably more than 40 vol.-% and especially preferably more than 50 vol.-% lithium disilicate crystals is preferred of. The term "main crystalline phase" means a crystalline phase having the highest proportion by volume compared to other crystalline phases.

According to the present invention, the blank with lithium silicate glass layer, lithium silicate glass layer with crystal nuclei or lithium metasilicate glass ceramic layer, and according to the present invention, the preferred embodiment of the blank with lithium disilicate glass ceramic layer Embodiments are described below.

Those blanks in which lithium silicate glass, lithium silicate glass with crystal nuclei, lithium metasilicate glass-ceramic and lithium disilicate glass-ceramic comprise given amounts of at least one of the following components and preferably all of the following components is preferred:

in

Me(I) ₂ O is selected from Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O or mixtures thereof,

Me(II)O is selected from CaO, BaO, MgO, SrO, ZnO and mixtures thereof,

Me(III) ₂ O ₃ is selected from Al ₂ O ₃ , La ₂ O ₃ , Bi ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ and mixtures thereof,

Me(IV)O ₂ is selected from ZrO ₂ , TiO ₂ , SnO ₂ , GeO ₂ and mixtures thereof,

Me(V) ₂ O ₅ is selected from Ta ₂ O ₅ , Nb ₂ O ₅ and mixtures thereof,

Me(VI)O ₃ is selected from WO ₃ , MoO ₃ and mixtures thereof, and

_The nucleating agent is selected from _P2O5 , metals and mixtures thereof.

Na ₂ O and K ₂ O are preferably Me(I) ₂ O, an oxide of a monovalent element.

CaO, MgO, SrO and ZnO are preferably oxides of divalent elements Me(II)O.

Al ₂ O ₃ , La ₂ O ₃ and Y ₂ O ₃ are preferably Me(III) ₂ O ₃ oxides of trivalent elements.

ZrO ₂ , TiO ₂ and GeO ₂ are preferably Me(IV)O ₂ oxides of tetravalent elements.

Ta ₂ O ₅ and Nb ₂ O ₅ are preferably Me(V) ₂ O ₅ oxides of pentavalent elements.

WO ₃ and MoO ₃ are preferably Me(VI)O ₃ , an oxide of a hexavalent element.

P ₂ O ₅ is preferably a nucleating agent.

Lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass ceramics and lithium disilicate glass ceramics contain _SiO2 and _Li2O , preferably 1.5 to 3.0, especially 2.0 to 2.8 and preferably 2.20 SiO ₂ and Li ₂ O to a molar ratio of 2.45.

In another preferred embodiment, lithium silicate glass, lithium silicate glass with crystal nuclei, lithium metasilicate glass ceramics and lithium disilicate glass ceramics comprise at least one of the following components in given amounts and preferably comprise All of the following components:

It is further preferred that the lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass ceramics and lithium disilicate glass ceramics contain colorants and/or fluorescent agents.

Examples of colorants are oxides of d-block and f-block elements such as Ti, V, Sc, Mn, Fe, Co, Ta, W, Ce, Pr, Nd, Tb, Er, Dy, Gd, Eu and Yb oxide. Metal colloids, such as those of Ag, Au and Pd, can also be used as colorants and additionally as nucleating agents. These metal colloids can be formed, for example, by reduction of the corresponding oxides, chlorides or nitrates during the melting and crystallization process.

Preferably, the blanks according to the invention are present in the form of blocks, disks or cylinders. In these forms it can be further processed with particular ease to form the desired dental restoration.

In a further preferred embodiment, the blank according to the invention has holding means for securing it in a processing device. The holding means secure the blank in a processing device, such as in particular a milling device or a grinding device. The retaining mechanism is usually in the form of a pin and preferably consists of metal or plastic.

The invention also relates to a method for producing blanks according to the invention.

The method for producing a blank according to the invention having an integral layer of lithium silicate glass, an integral layer of lithium silicate glass with nuclei or an integral layer of lithium metasilicate glass-ceramic is characterized in that

and

(ii) Bonding the layers to each other.

In a preferred embodiment of the method, the lithium silicate glass layer or the nucleated lithium silicate glass layer is converted into a nucleated lithium silicate glass layer or a lithium metasilicate glass ceramic layer. In particular, the conversion is achieved by at least one heat treatment. Preferred methods for converting lithium silicate glasses into nucleated lithium silicate glasses and further into corresponding lithium metasilicate glass ceramics and finally also into corresponding lithium disilicate glass ceramics have been described above. condition.

Particularly preferably, a plurality of lithium silicate glass layers or layers of nucleated lithium silicate glass are bonded to one another and converted into a plurality of lithium metasilicate glass-ceramic layers by at least one heat treatment. Conjugation and transformation can be performed in one step or also in different steps.

In order to produce monolithic layers arranged one above the other, lithium silicate glass is usually produced first. For this purpose, mixtures of suitable starting materials, such as mixtures of carbonates, oxides, phosphates and fluorides, are melted at temperatures in particular from 1300 to 1600° C. for 2 to 10 hours. In order to obtain a particularly high degree of homogeneity, the glass melt obtained is poured into water to form granulated glass material, and the granulated material obtained is subsequently melted again.

The obtained lithium silicate glass melt is then typically poured into a suitable mold to form the first integral layer. Then, generally in the same way, a second integral layer of a different color is prepared from another lithium silicate glass melt. The process can also be repeated to prepare other integral layers of different colors.

It is also possible to subject the obtained monolithic layer of lithium silicate glass to heat treatment, in particular at 500 to 600° C., in order to achieve the formation of nuclei for the crystallization of lithium metasilicate and/or lithium disilicate. An integral layer of nucleated lithium silicate glass then appears. Preferably, the heat treatment is performed for a period of 10 to 180 min. The layer is preferably cooled to room temperature in a controlled manner after the heat treatment. In particular, this achieves stress relief in the nucleated glass.

Then, the obtained monolithic layer of lithium silicate glass with crystal nuclei can be subjected to heat treatment, especially at 550 to 750° C., to achieve crystallization of lithium metasilicate. An integral layer of lithium metasilicate glass-ceramic then emerges. Preferably, the heat treatment is performed for a period of 5 to 60 minutes.

In stage (i) of the method according to the invention, the resulting monolithic layer of lithium silicate glass, the resulting monolithic layer of nucleated lithium silicate glass or the resulting monolithic layer of lithium metasilicate glass-ceramic is bonded to each other Arranged overlappingly. This can be achieved, for example, simply by stacking the layers on top of each other.

The plurality of integral layers are bonded together in stage (ii). This can be achieved in particular by heat treatment or by using a binding agent.

In a first preferred embodiment of the method according to the invention,

(a1) Applying one integral layer to the other integral layer in the melt.

In this way, not only are the two said layers arranged one above the other, but they are also bonded to each other.

An integral layer of lithium silicate glass is preferably used in this embodiment.

It is further preferred that one integral layer in melt form has a temperature of 1100 to 1500°C and the other integral layer has a temperature of 400 to 600°C. The temperature difference between the layers helps prevent mixing of the layers and helps prevent stresses in the blank.

In particular, the procedure is such that a first lithium silicate glass melt is prepared at in particular 1350 to 1500° C. and injected into a suitable mold to form an integral layer. The layer is cooled to a temperature of 400 to 600°C. A second lithium silicate glass melt is then poured over the first layer to form a second, differently colored layer. During this step, the layers fuse and are firmly bonded to each other.

It is also possible to obtain blanks with more than two layers by pouring onto a further lithium silicate glass melt.

Using the heat treatment described above, the lithium silicate glass can be converted into lithium silicate glass with crystal nuclei, lithium metasilicate glass ceramics and finally also into lithium disilicate glass ceramics to prepare corresponding blanks.

In a second preferred embodiment of the method according to the invention,

(b1) heating the plurality of integral layers arranged one above the other to a temperature of at least 500°C and in particular to a temperature in the range of 550 to 750°C.

Preferably, a nucleated lithium silicate glass layer is used.

Fusion at the boundary surfaces and thus layer-to-layer bonding occurs due to the action of heat. In particular, the heating is carried out for a period of 5 to 60 min.

It is particularly advantageous that, as a result of the heating, not only the bonding of the layers but also the crystallization of the lithium metasilicate is achieved. In order to achieve crystallization, the layer is heated to, in particular, 550 to 750°C. It is also possible first to achieve the bonding of the layers at a temperature gradually rising from room temperature, and to subsequently achieve its crystallization at a temperature suitable for the formation of metasilicate.

Thus, also with this embodiment, preforms having a lithium metasilicate glass-ceramic layer can be produced particularly easily.

Particularly preferably, the plurality of layers are pressed together during heating under a pressure of in particular 0.01 to 4.0 MPa.

It is further preferred to smooth the surfaces of the layers facing each other. This can be achieved by customary grinding and polishing. In particular, diamond grinding discs and silicon carbide (SiC) abrasive paper can be used as grinding and polishing tools.

For a smooth surface, generally a low pressing pressure of, eg, about 0.01 MPa at most is required to achieve good bonding of the multiple glass layers. For non-smooth surfaces, a pressing pressure of 1 to 4 MPa is usually applied.

This pressing pressure is applied to the stacked layers in particular by polished surfaces _{of Si3N4} , steel, graphite, _Al2O3 and/or ZrO2. A release agent such as boron nitride (BN) may also be used to prevent the layer from sticking to the indenter. Indenters with embossed reliefs can also be used.

The layers used may in particular be cast layers of suitable dimensions or even large plates or rods from which layers of suitable dimensions may be cut.

In a third preferred embodiment of the method according to the invention,

(c1) A bonding agent is provided between a plurality of the integral layers.

In particular, glass solders, crystal glass solders, glass ceramic solders or adhesives come into consideration as bonding agents.

Glass solders, crystallized glass solders and glass-ceramic solders come into consideration, especially glasses and glass-ceramics which melt at low temperatures and in particular at temperatures from 550 to 750° C. They are usually applied as powders, tablets or pastes to the layers to be bonded. Due to the temperature treatment, the solder melts and coats the surface of the layer. After cooling, the secure bond provided by the solder in this way is formed between the layers. Preferably, a plurality of integral layers provided with solder and arranged one above the other are heated to the melting temperature of the solder.

By heating the solder, crystallization of the lithium metasilicate in the layer can also take place simultaneously. To achieve this crystallization, heating is carried out to in particular 550 to 750°C. It is also possible first to effect the melting of the solder and thus the bonding of the layers at a temperature gradually increasing from room temperature, and subsequently to effect its crystallization at a temperature suitable for the formation of lithium metasilicate.

In particular, polymerizable binders with glass as filler come into consideration as binders. Those glass fillers which crystallize upon heat treatment are preferred. Particular preference is given to using as filler those glasses which have a similar composition to the glass of one of the layers to be bonded or to a mixture of the glasses of the layers to be bonded.

The adhesive is applied to at least one of the layers to be bonded, for example by coating. The layers are arranged one above the other and the adhesive is subsequently cured in a conventional manner. In this way, a blank of joined layers is obtained which can be further processed to form a dental restoration.

Preferably, the multiple layers of lithium silicate glass, nucleated lithium silicate glass and lithium metasilicate glass-ceramic are bonded using an adhesive.

A blank having a lithium silicate glass layer, a nucleated lithium silicate glass layer or a lithium metasilicate glass-ceramic layer produced according to the method according to the invention can easily be converted into a blank having a lithium disilicate glass-ceramic layer. The convertibility of the precursors lithium silicate glass, lithium silicate glass with crystal nucleation and lithium metasilicate glass ceramics to lithium disilicate glass ceramics has been described above.

The method for producing a blank with a lithium disilicate glass-ceramic layer according to the invention is characterized in that

(iii) subjecting the blank according to the present invention having a lithium silicate glass layer, a lithium silicate glass layer with crystal nuclei and a lithium metasilicate glass-ceramic layer to at least one heat treatment, so that the lithium silicate glass, with crystal nuclei Lithium silicate glass or lithium metasilicate glass ceramics are converted into lithium disilicate glass ceramics.

Preferably, the heat treatment is subjected to the nucleated lithium silicate glass layer or the blank having the lithium metasilicate glass ceramic layer.

Preferably, said heat treatment is carried out at a temperature of at least 750°C, and in particular at a temperature in the range of 750 to 950°C.

Due to the properties of these blanks according to the invention, they are particularly suitable for further processing to form dental restorations.

Therefore, the present invention also relates to a method for manufacturing a dental restoration, wherein

(d1) imparting the shape of the blank dental restoration according to the invention having a lithium silicate glass layer, a lithium silicate glass layer with crystal nuclei or a lithium metasilicate glass ceramic layer by machining;

(d2) performing at least one heat treatment to convert lithium silicate glass, nucleated lithium silicate glass, or lithium metasilicate glass-ceramic into lithium disilicate glass-ceramic; and

(d3) Optionally, finishing the surface of the obtained dental restoration.

or in an alternative implementation

(e1) imparting shape to the blank dental restoration with the layer of lithium disilicate glass-ceramic according to the invention by machining; and

(e2) Optionally, finishing the surface of the obtained dental restoration.

A custom-shaped dental restoration can be obtained by simple machining from the blank according to the invention. For this purpose, in particular blanks having nucleated lithium silicate glass layers (d1), lithium metasilicate glass ceramic layers (d1) or lithium disilicate glass ceramic layers (e1) are used.

The machining in stages (d1) and (e1) is generally carried out by material removal processes, and in particular by milling and/or grinding. Preferably, said machining is performed using a computer controlled milling and/or grinding device. Particularly preferably, the machining is carried out as part of a CAD/CAM process.

In stage (d2), the blank is subjected to a heat treatment to achieve a controlled crystallization of lithium disilicate, forming a lithium disilicate glass-ceramic. In particular, heat treatment is performed at a temperature of 750 to 950°C, and preferably 800 to 900°C. In particular, the heat treatment is performed for a period of 1 to 30 min, and preferably 2 to 15 min.

Heat treatment can also be used to burn off binders used during the preparation of the blanks used. However, it is also possible to burn out the binder as a separate step preceding the crystallization step of the lithium disilicate in stage (d2).

It was particularly surprising that, in particular, the crystallization of lithium disilicate also occurred along the interfaces of the layers, as can be determined by scanning electron microscopy (SEM examination). Presumably, this phenomenon greatly contributes to the secure bond between the layers and effectively counteracts the weakening of the obtained dental restoration at this interface.

After carrying out stages (d2) and (e1), a dental restoration with a lithium disilicate glass-ceramic layer is obtained which has good mechanical properties and high chemical stability. Furthermore, due to said multiple layers of different colours, it provides a good imitation of the optical properties of natural tooth material, such as a good imitation of the dentin to incisal color transition. Finally, restorations can also be produced from blanks according to the invention without substantial shrinkage. This is due in particular to the fact that the blank according to the invention has integral layers and no discontinuous layers, such as layers of powder or granular material. Such discontinuous layers must also be densely sintered to provide the final restoration, which is accompanied by significant shrinkage. Thus, by using the blank according to the invention, dental restorations with exact desired dimensions can be easily produced.

Preferably, the dental restoration manufactured according to the invention is selected from the group consisting of crowns, abutments, abutment crowns, inlays, onlays, veneers, shells and bridges, and coverings for multi-part restoration frameworks structure, the frame can consist, for example, of oxide ceramics, metals or dental alloys.

In optional phases (d3) and (e2), the surface of the dental restoration can also be finished. In particular, it is also possible to enamell the dental restoration or polish the dental restoration at a temperature of 700 to 850°C.

Furthermore, layered materials of glass and/or glass ceramics can also be applied.

Finishing with glaze and crystallization of lithium disilicate can naturally also be carried out in one step.

Due to the above-mentioned specific properties of the blank according to the invention, it is particularly suitable for the manufacture of dental restorations. The invention therefore also relates to the use of said blanks for the manufacture of dental restorations, in particular crowns, abutments, abutment crowns, inlays, onlays, veneers, shells and bridges, and covering structures.

The invention is explained in more detail below with the aid of examples.

Example

These examples illustrate in particular the preparation of two-layer blanks. In a similar manner, blanks with more than 2 and up to 10 layers of different colors can be produced. The order of the layers is chosen to mimic the color, opalescence, and translucency transitions of natural tooth material as naturally as possible.

Example 1 - Melting and casting process

This example describes the preparation of a blank in the shape of a block with 2 monolithic layers of lithium silicate glass of different colors according to the invention, its nucleation in the glass and its transformation into a lithium metasilicate glass-ceramic and processing blocks with lithium metasilicate glass-ceramic layers to form highly esthetic dental restorations made of lithium disilicate glass-ceramic.

Two kinds of lithium silicate glasses having the following compositions were melted.

Glass 1:

Composition in wt.-%

74.36 SiO ₂ , 3.26 K ₂ O, 15.45 Li ₂ O, 3.55 Al ₂ O ₃ , 3.38 P ₂ O ₅

Glass 2:

Composition in wt.-%

70.64 SiO ₂ , 3.09 K ₂ O, 14.68 Li ₂ O, 3.38 Al ₂ O ₃ , 3.21 P ₂ O ₅ , 3.00 ZrO ₂ , 2.00 Colored oxides

First, the glass is melted from suitable starting materials at 1450 to 1500°C. After sufficient homogenization, the melt from glass 1 was poured into graphite molds to form an integral layer and the layer was cooled to 500 to 550° C. within 30 to 60 seconds. The melt of glass 2 is then poured into graphite molds and poured on top of the cooled glass layer. In this way, a homogeneous fusion of the two glass layers is achieved without additional pressing pressure. Multiple other layers of glass can be poured in a similar manner to that described.

Glass blocks of at least two layers removed from the mold were subjected to a heat treatment in a furnace at 500° C. for 10 min to nucleate and cooled to room temperature in a controlled manner.

The block was then subjected to a heat treatment at 650° C. for 20 min to achieve a controlled crystallization of lithium metasilicate in the layer. A block with a lithium metasilicate glass-ceramic layer is obtained.

A SEM image of a cross-section through a lithium metasilicate-containing block is shown in Figure 1 after treating the surface 8s with an aqueous HF solution to slightly etch the crystalline phase and make the structure visible. Good bonding of the layers at the boundary surfaces and crystallization on the boundary surfaces are shown.

This block can be given the shape of a dental restoration by means of CAD/CAM processes. Lithium disilicate is precipitated by subsequent heat treatment at 850° C. for 10 min to obtain the desired high strength dental restoration which has an appearance similar to natural teeth due to its multiple layers of different colours.

A SEM image of a section through a bulk with precipitated lithium disilicate is shown in FIG. 2 after treating the surface with HF vapor for 30 s to slightly etch the crystalline phase and visualize the structure. Surprisingly, a very homogeneous structure can be observed on the boundary surface, which leads to an almost complete disappearance of the boundary surface. The production of several different layers of glass can only be discerned from the different colors of the layers.

Example 2 - Using Temperature and Pressure to Bond Multiple Glass Layers

From 2 to 10 glass plies are formed into monolithic blanks in a thermal bonding process at 500 to 750° C. under a pressure of 0.01 to 4 MPa. Thanks to this heat treatment, it is possible not only to bond the different glass layers but also to crystallize them.

Example 2A: polished surface, low pressure -0.01MPa

(a) Preparation of glass layer with crystal nuclei

First, two kinds of lithium silicate glasses having the following compositions were melted at 1450 to 1500°C.

Glass 3:

Composition in wt.-%

70.68 SiO ₂ , 4.00 K ₂ O, 14.68 Li ₂ O, 3.38 Al ₂ O ₃ , 3.21 P ₂ O ₅ , 0.26 MgO, 0.85 ZrO ₂ , 2.94 colored oxide

Glass 4:

Composition in wt.-%

70.99 SiO ₂ , 4.74 K ₂ O, 14.76 Li ₂ O, 1.49 Al ₂ O ₃ , 3.28 P ₂ O ₅ , 0.70 ZnO, 0.99 ZrO ₂ , 3.05 Colored oxide

The two melts obtained are then separately poured into two molds to form two glass layers with desired dimensions.

The two glass layers were heat-treated at 500° C. for 10 min to form crystal nuclei. They are then cooled to room temperature in a controlled manner.

Then, the surfaces of the two glass layers to be bonded are ground and polished precisely in parallel. For this purpose, it was first ground plane-parallel with a 74-μm diamond disc, then treated with a 20-μm diamond disc in the first polishing step, and then treated with 1000-grit SiC sandpaper in the second polishing step . The two surfaces obtained are cleaned with water, optionally also with ethanol or acetone.

(b) Combined glass layer and crystallization of lithium metasilicate

The two glass plies are arranged precisely one above the other and pressed together at a pressure of 0.01 MPa by the action of a force perpendicular to the surfaces to be bonded. The pressed glass plies are then heated to 650° C. within 25 min from 400° C. to achieve bonding of the layers. Crystallization of lithium metasilicate was then induced by maintaining a temperature of approximately 650 to 660° C. for 20 min. The crystallized mass obtained is then cooled to room temperature in a controlled manner.

A SEM image of a section through a block with lithium metasilicate is shown in FIG. 3 after treating the surface 8s with aqueous HF to slightly etch the crystalline phases to make the structure visible. The image also shows very good bonding of layers and initiation of crystallization on boundary surfaces.

(c) Machining and crystallization of lithium disilicate

The obtained block with different lithium metasilicate glass-ceramic layers can be easily machined using a conventional CAM unit, such as the Cerec MC XL from Sirona, to give the block the desired shape of the dental restoration.

After machining, the lithium metasilicate glass-ceramic was converted into a lithium disilicate glass-ceramic by heat treatment at 850° C. for 10 min. A dental restoration with the sought after final strength is thus obtained. Furthermore, the dental restoration has a very attractive appearance in the form of a color gradient corresponding to the dentin to incisal color transition.

The SEM image of the cross-section of the unmachined block with lithium disilicate after 30 s of treating the surface with HF vapor is shown in FIG. 4 . Here too, a very homogeneous structure can surprisingly be observed at the interface, which leads to the almost complete disappearance of the interface. The production of several different layers of glass can only be discerned from the different colors of the layers.

Example 2B: Unpolished surface, high pressure -1.5MPa

Example 2A was repeated. But the surfaces of the glass layers were not ground, and they were bonded together and crystallized under a higher pressure of 1.5 MPa and by a modified heat treatment to form lithium metasilicate glass-ceramic.

During this heat treatment, the glass plies that have been pressed together are heated from 550° C. to 680° C. within 2 minutes to achieve bonding of the layers. Crystallization of lithium metasilicate was then induced by maintaining a temperature of about 680° C. for about 20 min. Afterwards, the obtained crystallized mass is cooled to room temperature in a controlled manner.

The SEM image of the section through the block with lithium metasilicate after treating the surface with aqueous HF for 8 s is shown in FIG. 5 . The image also shows very good bonding of the layers.

After machining, the lithium metasilicate glass-ceramic was converted into a lithium disilicate glass-ceramic by heat treatment at 850° C. for 10 min. A dental restoration with the desired final strength is thus obtained. Furthermore, the dental restoration has a very attractive appearance in the form of a color gradient corresponding to the dentin to incisal color transition.

A SEM image of a cross-section of an unmachined block with lithium disilicate is shown in FIG. 6 after treating the surface with HF vapor for 30 s. Here too, surprisingly, a very homogeneous structure can be observed on the boundary surface, which leads to the almost complete disappearance of the boundary surface. The production of several different glass layers can also be discerned only from the different colors of the layers.

Example 3 - Bonding glass layers by means of solder

In a similar manner to Example 2A, different nucleated glass layers were produced from Glass 3 and Glass 4 .

Powdered sintered glass solder with an average pore diameter _D50 of 6 to 10 μm relative to the number of particles is applied to the surfaces to be bonded of two different nucleated glass layers and the coated surfaces are placed exactly one above the other .

The glass layers are then subjected to a controlled multi-step heat treatment. The glass layer was heated from room temperature to 700° C. at a rate of 10 K/min, kept at this temperature for 10 min, and then cooled again to room temperature at a rate of about 20 K/min. A vacuum of about 50 mbar was applied starting at about 550° C. until the end of the hold time. Sintering active glass solder melts due to heat treatment and bonds them by coating the glass surfaces. Likewise, during heat treatment, lithium metasilicate crystals form in the volume of the glass layer. The obtained block with the lithium metasilicate glass-ceramic layer is then cooled in a controlled manner.

can be achieved by using a conventional CAM unit such as the one from Sirona The MC XL machines the block to easily give the block the shape of the dental restoration.

After machining, the lithium metasilicate glass-ceramic was converted into a lithium disilicate glass-ceramic by heat treatment at 850° C. for 10 min. A dental restoration with the sought after final strength is thus obtained. Furthermore, the dental restoration has a very attractive appearance in the form of a color gradient corresponding to the dentin to incisal color transition.

Example 4 - Bonding glass layers by means of an adhesive

First, different nucleated glass layers were prepared from Glass 3 and Glass 4 in a similar manner to Example 2A.

These glass layers are then subjected to a controlled multi-step heat treatment. The glass layer was heat-treated at 500°C for 10 minutes to form crystal nuclei of lithium metasilicate. A further heat treatment is then carried out at 650° C., which causes lithium metasilicate to form as the main crystalline phase in the volume of the glass layer. The obtained lithium metasilicate glass-ceramic layer is then cooled in a controlled manner.

The following composite adhesive with crystalline glass filler is applied to the surfaces to be bonded of the glass-ceramic layers and the layers are laid down precisely one above the other.

Dual-cure composite adhesive with crystalline glass filler component:

Composite material with 60 wt.-% crystalline glass filler (d ₅₀ <10 μm, preferably d ₅₀ =7 μm)

Composition of composite material in wt.-%:

Composition of crystalline glass filler in wt.-%:

70.82 SiO ₂ , 4.37 K ₂ O, 14.72 Li ₂ O, 2.44 Al ₂ O ₃ , 3.25, P ₂ O ₅ , 0.13 MgO, 0.35 ZnO, 0.92 ZrO ₂ , 3.00 Colored oxide

After curing of the binder, a block with two lithium metasilicate glass-ceramic layers forms, which can be machined analogously to Example 3 and is transformed by crystallization of lithium disilicate into a high-strength and optionally very attractive Human dental restorations. During the heat treatment used for the crystallization of lithium disilicate and the bonded glass-ceramic layers, the composite material is completely thermally decomposed. The crystalline glass filler also acts as a sintered glass solder.

Example 5

Further multilayer blanks were prepared analogously to Examples 1 to 4 and processed by means of CAD/CAM technology to form dental restorations. The glasses listed in Table 1 below were used. With their help, it is likewise possible to achieve a good combination of overall layers and very good color gradations of several layers.

Table 1:

glass 5 glass 6 glass 7 glass 8 glass 9 glass 10 glass 11 components wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO ₂ 71.52 71.39 72.09 71.02 69.20 69.76 71.16 K ₂ O 4.21 4.20 4.24 4.29 3.80 3.70 4.19 SrO 0.00 1.00 0.00 0.99 0.00 0.00 0.00 Li ₂ O 14.89 14.86 15.01 14.78 15.10 15.00 14.81 Al ₂ O ₃ 3.31 1.17 3.33 1.16 3.40 2.00 3.29 P ₂ O ₅ 3.27 3.28 3.30 3.27 3.30 3.50 3.25 MgO 1.00 0.00 1.01 0.00 0.00 0.00 1.00 _ZrO2 0.80 2.00 0.00 1.99 0.60 2.00 0.00 ZnO 0.00 1.00 0.00 1.40 2.00 2.00 0.00 _CeO2 0.50 0.60 0.51 0.60 1.70 0.60 1.70 La ₂ O ₃ 0.00 0.00 0.00 0.00 0.30 1.00 0.00 V ₂ O ₅ 0.00 0.00 0.00 0.00 0.10 0.04 0.10 Tb ₄ O ₇ 0.50 0.50 0.51 0.50 0.50 0.40 0.50

Selected properties of these glasses and glass-ceramics prepared from them are listed in Table 2 below.

Table 2:

Color value:

Using a color measuring device (Minolta CM3700D), the color value was determined with a 2 mm-thick sample of crystalline glass ceramic. The measured L*, a* and b* values showed that the glass-ceramic could be stained with typical dentin colors. The CR value (contrast ratio) is a measure of translucency. The obtained contrast values between 50% and 83% demonstrate that a gradient from incisal (high translucency) to dentin (less translucent) is possible without problems.

DSC evaluation:

The characteristic temperature of the glass is given. Tg means glass transition. E1 represents the first exothermic reaction associated with the crystallization of the lithium metasilicate phase. E2 represents the second exothermic reaction associated with the crystallization of the lithium disilicate phase. Ts represents the melting temperature of the lithium disilicate phase.

It has been shown that it is advantageous for a good bond between the glasses to be bonded and the glass-ceramics if these temperatures differ only slightly from each other between the glasses used and the glass-ceramics, as is the case for example with glasses 5 to 11 like that.

Coefficient of Thermal Expansion (CTE):

CTE describes the thermal expansion behavior of glass ceramics. It is advantageous for the stress-free bonding of the glass ceramics if the glass ceramics bonded to one another have similar coefficients of expansion.

The molar ratio of:

The molar ratio of SiO ₂ to Li ₂ O affects the proportion of the crystal phases formed.

Crystal phase part:

The crystal phase part of lithium metasilicate (LS) basically determines the processing performance of the billet. The crystalline phase fraction of lithium disilicate (LS2) is very important for the performance of the final restoration.

strength:

Strength was determined according to ISO 6872:2008 using "two-way bending test specimens" from the respective lithium disilicate glass-ceramics.

Example 6

The glasses listed in Table 3 below were also processed similarly to Examples 1 to 4 to form multilayer blanks and ultimately dental restorations.

Selected properties of these glasses and glass-ceramics prepared from them are listed in Table 4 below. These properties were determined in a similar manner to Example 5.

With glass 15, no lithium metasilicate (LS) crystallized, but lithium disilicate (LS2) crystallized already at a temperature of 711°C. Thus, after nucleation (500° C./10 min), machining conveniently takes place already.

Like glass 15, glass 18 also does not form any LS. LS2 has crystallized at 670°C.

After the first crystallization, glass 19 shows only a small amount of lithium metasilicate crystal phase. The lithium disilicate glass-ceramic that emerges after the second crystallization has a very high translucency.

Example 7

Similar to Example 3, a glass of the following composition was used as a sintered glass solder to bond together layers of nucleated glass according to Table 1 at 690°C.

components wt.-% SiO ₂ 64.65 K ₂ O 7.29 Na ₂ O 6.75 SrO 2.22 Li ₂ O 2.07 CaO 1.29 Al ₂ O ₃ 6.61 B ₂ O ₃ 1.71 TiO ₂ 1.45 _ZrO2 0.60 ZnO 3.08 _CeO2 0.56 f 1.72

Claims (26)

1. Blanks for dental purposes having at least 2 bonded to each other Lithium silicate glass layer, Lithium silicate glass layer with nuclei or Lithium metasilicate glass-ceramic layer, Wherein the layers are of different colors and the layers are integral. 2. The blank according to claim 1, which has a lithium silicate glass layer or a lithium metasilicate glass ceramic layer with crystal nuclei. 3. Blank according to claim 1 or 2, wherein the lithium metasilicate glass-ceramic contains lithium metasilicate as the main crystalline phase, and in particular more than 5 vol.-%, preferably more than 10 vol.-% and especially More than 20 vol.-% of lithium metasilicate crystals are preferred. 4. Blanks for dental purposes having at least 2 lithium disilicate glass-ceramic layers bonded to each other, Wherein the layers are of different colors and the layers are integral. 5. The blank according to claim 4, wherein the lithium disilicate glass-ceramic contains lithium disilicate as main crystalline phase, and in particular more than 30 vol.-%, preferably more than 40 vol.-% and particularly preferably more than 50 vol.-% lithium disilicate crystals. 6. The blank according to any one of claims 1 to 5, wherein the lithium silicate glass, lithium silicate glass with crystal nucleus, lithium metasilicate glass-ceramic and lithium disilicate glass-ceramic comprise the given Quantitative amounts of at least one and preferably all of the following components: in Me(I) ₂ O is selected from Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O or mixtures thereof, Me(II)O is selected from CaO, BaO, MgO, SrO, ZnO and mixtures thereof, Me(III) ₂ O ₃ is selected from Al ₂ O ₃ , La ₂ O ₃ , Bi ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ and mixtures thereof, Me(IV)O ₂ is selected from ZrO ₂ , TiO ₂ , SnO ₂ , GeO ₂ and mixtures thereof, Me(V) ₂ O ₅ is selected from Ta ₂ O ₅ , Nb ₂ O ₅ and mixtures thereof, Me(VI)O ₃ is selected from WO ₃ , MoO ₃ and mixtures thereof, and _The nucleating agent is selected from _P2O5 , metals and mixtures thereof. 7. The blank according to any one of claims 1 to 6, wherein said lithium silicate glass, lithium silicate glass with crystal nuclei, lithium metasilicate glass-ceramic and lithium disilicate glass-ceramic comprise the given Quantitative amounts of at least one and preferably all of the following components: 8 . The blank as claimed in claim 1 , which has holding means for a processing device, wherein the holding means in particular consist of metal or plastic. 9. be used for preparing according to any one of claim 1 to 3 or 6 to 8, have lithium silicate glass layer, lithium silicate glass layer with crystal nucleus or the blank of lithium metasilicate glass-ceramic layer method, where (i) a plurality of monolithic layers of lithium silicate glass, monolithic layers of lithium silicate glass with crystal nuclei, or monolithic layers of lithium metasilicate glass-ceramic are arranged on top of each other; and (ii) Bonding these layers to each other. 10. The method according to claim 9, wherein the lithium silicate glass layer or the lithium silicate glass layer with crystal nuclei is converted into a lithium silicate glass layer with crystal nuclei or a lithium metasilicate glass-ceramic layer, and In particular it is converted by at least one heat treatment. 11. The method according to claim 10 , wherein a plurality of lithium silicate glass layers or nucleated lithium silicate glass layers are bonded to each other and converted into a plurality of lithium metasilicate glass ceramics with lithium metasilicate glass ceramics by at least one heat treatment. layer to prepare a blank with multiple lithium metasilicate glass-ceramic layers. 12. A method according to any one of claims 9 to 11, wherein, (a1) Applying one integral layer to the other integral layer in the melt. 13. The method of claim 12, wherein an integral layer of lithium silicate glass is used. 14. The method of claim 13, wherein the temperature of one integral layer is 1100 to 1500°C and the temperature of the other integral layer is 400 to 600°C. 15. The method according to any one of claims 9 to 11, wherein, (b1) heating the plurality of integral layers arranged one above the other to a temperature of at least 500° C. and in particular to a temperature of 550 to 750° C. 16. The method according to claim 15, wherein, in step (b1), the plurality of plies are laminated together at a pressure of in particular 0.01 to 4.0 MPa. 17. A method according to claim 15 or 16, wherein surfaces of the plurality of layers facing each other are smoothed. 18. The method according to any one of claims 9 to 11, wherein, (c1) providing a bonding agent between the plurality of integral layers. 19. The method according to claim 18, wherein the bonding agent is glass solder, crystallized glass solder, glass ceramic solder or an adhesive. 20. A method for preparing a blank having a lithium disilicate glass-ceramic layer according to any one of claims 4 to 8, wherein (iii) making the blank having a lithium silicate glass layer, a lithium silicate glass layer with crystal nuclei, and a lithium metasilicate glass-ceramic layer according to any one of claims 1 to 3 or 6 to 8 undergo at least one Heat treatment to convert lithium silicate glass, lithium silicate glass with nuclei, or lithium metasilicate glass-ceramic into lithium disilicate glass-ceramic. 21. The method according to claim 20, wherein a blank having a nucleated lithium silicate glass layer or a lithium metasilicate glass ceramic layer is subjected to the heat treatment. 22. The method according to claim 20 or 21, wherein the heat treatment is carried out at a temperature of at least 750°C, and in particular at a temperature of 750 to 950°C. 23. A method for the manufacture of dental restorations, wherein, (d1) The blank having a lithium silicate glass layer, a lithium silicate glass layer with crystal nuclei, or a lithium metasilicate glass-ceramic layer according to any one of claims 1 to 3 or 6 to 8 by machining the shape of the dental restoration; (d2) performing at least one heat treatment to convert lithium silicate glass, nucleated lithium silicate glass, or lithium metasilicate glass-ceramic into lithium disilicate glass-ceramic; and (d3) Optionally, finishing the surface of the obtained dental restoration, or (e1) imparting by machining a shape to a blank dental restoration having a lithium disilicate glass-ceramic layer according to any one of claims 4 to 8; and (e2) Optionally, finishing the surface of the obtained dental restoration. 24. A method according to claim 23, wherein said machining is performed using a computer controlled milling device and/or grinding device. 25. The method according to claim 23 or 24, wherein the dental restoration is selected from the group consisting of crowns, abutments, abutment crowns, inlays, onlays, veneers, shells, bridges and overlay structures . 26. The blank according to any one of claims 1 to 8 for the production of dental restorations and in particular crowns, abutments, abutment crowns, inlays, onlays, veneers, casings, bridges and use of overlay structures.